Weight and balance indicator



Aug. 21, 1956 BLACKMON ET AL 2,759,356

WEIGHT AND BALANCE INDICATOR Original Filed Nov. 13, 1945 4 Sheets-Sheet1 Ava/we; few/7M5; MzMm A/vo 1 F/IM/M 0 aenaz Aug. 21, 1956 T. M.BLACKMON ETAL 2,759,356

WEIGHT AND BALANCE INDICATOR Original Filed Nov 4 Sheets-Sheet 2 Aug.21, 1956 T. M. BLACKMON ETAL 2,759,356

WEIGHT AND BALANCE INDICATOR Original Filed Nov. 15, 194.5 4Sheets-Sheet 3 Aug. 21, 1956 T. M. BLACKMON ETAL 2,759,356

' WEIGHT AND BALANCE INDICATOR Original Filed Nov. 13. 194.5 4Sheets-Sheet 4 55 7 20/14 5144764 2 fl V/i/f- F i 6 E- A 77'azA/E%United States Patent WEIGHT AND BALANCE INDICATOR Tructt M. Blackmon,Sherman Oaks, and Firmin D. Porter, Venice, (Ialifi, assignors toDouglas Aircraft Company, Inc, Santa Monica, Calif.

Original application November 13, 1945, erial No. 628,1dtl, now PatentNo. 2,615,330, dated October 28, 1952. Divided and this applicationOctober 20, 1952, Serial No. 317,725

7 Claims. (Cl. 73-65) This invention relates to apparatus for indicatingthe weight and balance conditions of a vehicle as they change during theloading of the vehicle. This application is a division of ourapplication Serial No. 628,190, filed November 13, i945, now Patent No.2,615,330.

Devices of this general type are particularly useful in aircraft, forindicating at some suitable station, such as the pilots cockpit or thebaggage compartment, such loading-induced variables as the total weightof the aircraft, the longitudinal location of its center of gravity, orthe weight on each of the landing wheels thereof for purposes ofcomparison. It is to be understood, however, that the present inventionis by no means limited in the scope of its utility to employment withaircraft, being equally well applicable to automobiles and otherconveyances will become apparent hereinafter.

Previous devices of this general nature, and particularly those employedin connection with aircraft, are constructed to operate in response toloading-induced motions of, or pressure changes in, certain hydrauliccomponents, such as the landing gear struts. Due to the alternatebinding and releasing action of their packing glands and the variablebehavior of the fluid in the struts, these motions are not linearlyproportional to the load changes nor immediately responsive thereto,instead being discontinuous and quite jerky. The motivating force foractuating the indicating component of the apparatus hence being erratic,such apparatus is unpredictable and unreliable in operation.

Prior devices employing electrical means for effecting indication of theloading-induced variables of a vehicle are usually quite complex anddelicate and hence unreliable.

it is the general object of this invention to provide a vehicleloading-indicating device which will be directly and continuouslyresponsive to deflections of those structural components of the vehiclesground-engaging members which undergo movement in direct linearproportion to the increments in loading of the vehicle, wherebyimmediate and continuous indication will be made of the changing weightand balance conditions effected by loading the vehicle.

lt is a particular object of the invention to provide a device includingrelatively simple and reliable electrical means for electricallymeasuring the deflections of those components of the ground-engaginggear of vehicles which de; cct linearly proportionately to theincrements of loading on the vehicle, by causing them to actuateelectrical indicating means, responsive to relative changes ofelectromagnetic fields associated with said load-deflectable components.The indicating means of the device may be constructed and calibrated asa single device for quantitatively evaluating changes in the weight andthe longitudinal position of the center of gravity of the vehicle duringloading, or may consist of separate indicators enabling mutualcomparisons to obtain these values.

It is a specific object of the invention to provide a directly readableaircraft loading indicator which will be directly and immediatelyresponsive to the flexures of the axles of the landing wheels of theaircraft. Independence from the relatively erratic actuating forcefurnished by movement of, or pressure changes in, such variablyresponsive means as hydraulic struts, or the like, is thus assured whileenabling rapid and accurate indication of the total weight of theaircraft, or the longitudinal position of the center of gravity thereof;or the weight loading on each landing leg. I j

A further particular object of the invention is to provide aloading-indicating device of this improved nature, the calibration ofwhich will remain dependable without recalibration for relatively longperiods of time.

Still another particular object is to provide an indicating device ofthis type which will be substantially independent of the ground attitudeof the craft or of side thrusts on the landing gear, and of thermaleffects due either to altitude or climate.

Another particular object of the invention is to provide a device ofthis improved nature which will be relatively simple in construction andeasy to install on the vehicle in a permanent location with all itsparts carried in the vehicle.

With these and other objects in view, the invention essentiallyincludes, in one of its presently preferred embodiments, a flexuralelement in each ground-engaging member of the vehicle, load-deflectablein linear proportion to increments of loading of thevehicle and changingthe position of the armature of an electromagnetic displacement deviceassociated with each ground-engaging member, the displacement deviceconstituting one-half of a balanced bridge connected to the vehiclesenergy source and to the other half of the bridge, the armaturetherefore functioning to unbalance the bridge. The output voltages ofthe thus unbalanced bridges are sensitivity equalized and inductivelyimpressed upon one electrical side or the other, depending upon theindication sought, of a null-point sensitive volt meter, nullable on theother electrical side by a potentiometer energizable from the vehiclesenergy source and mechanically connected to a dial calibrated in poundsto indicate loading and in percentages of the M. A. C. for indicatinglongitudinal positions of the center of gravity. The outputs of thebridges are rendered connectible to the volt meter and to thepotentiometer in two different circuits, one of which effects additionin phase of the voltage outputs of the bridges to give an indication ofthe total weight, the other circuit eflecting a bridge-ratio comparisonof the voltage outputs from the forwardly located ground-engagingmembers and the rearwardly located ground-engaging members in such a wayas to indicate the longitudinal position of the center of gravity of thevehicle. if desired, the voltage-responsive indicating devices maybeseparate and the readings from the forwardly located wheel or wheelscompared by the vehicle operator to those from the rearwardly locatedwheels to obtain an evaluation of the longitudinal position of thecenter of gravity of the vehicles; or they may be added by hirntoindicate the total loading. I

The invention also provides novel methods of ascertaining the loading ofa vehicle and the longitudinalposition of its center of gravity. V

The other objects and accomplishments of the invention will be mademanifest as this specification proceeds.

The invention is illustrated in the accompanying'drawings, and describedhereinafter, in connection with its embodiment in airplanes, but it isto be understood that the inventive concepts are limited in theembodiments they can assume, only by the scope of the annexed claims.

In these drawings:

Figure 1 is a fragmentary perspective of an airplane, diagrammaticallyillustrating the general arrangement therein of the presently preferredembodiment of the invention;

Figure 2 is a diagrammatic view of the apparatus showing the axles ofthe aircraft, and one form of displacement device therein inlongitudinal section and illustrating respective circuits actuatedthereby for alternatively integrating or comparing the bridge outputs;

Figure 3 is a diagrammatic view of a modification showing circuits forenabling individual comparison of the loading on each landing leg;

Figure 4 is a fragmentary detailed view of an axle showing a modifiedarrangement of the fixed and the movable members of the displacementdevice adapted to compensate for thermal expansion;

Figure 5 is a fragmentary diagrammatic representation of optional meansfor resistively and reactively balancing each bridge; and

Figure 6 is a fragmentary diagrammatic view of another optional meansfor resistively and reactively balancing each bridge.

The invention will be exemplified in connection with its employment witha transport airplane having tricycle landing gear, and in its broadaspects, it is primarily predicated upon electrically measuring thedeflections of the axles of the tricycle landing gear thereof, inducedby increments of loading of the airplane. Preferably, the inventioninvolves the employment of displacement devices associated with theaxles and with balanced bridges adapted to be unbalanced byloading-induced deflections of the axles to impress voltages insummation or in ratio upon coordinated indicating devices adapted toindicate either the total loading, or the longitudinal position n of thecenter of gravity, of the airplane.

In such embodiment, the general arrangement comprises electromagneticdisplacement devices 10, one of these devices being associated with theaxle of each landing wheel, the devices being electrically connected inparallel with each other and with the airplanes source of electricalenergy 11. The connections comprise an operating circuit 12 leading fromthe energy source to a junction box 13, from which respective feedercircuits 14, 15, and 16 lead to the respective electromagnetic devices.Conductors 17, associated with bridge balancing and transformer couplingmeans, hereinafter detailed, also extend from the respectiveelectromagnetic devices to the junction box.

The location of the junction box is a matter of preference, but can beadvantageously situated in the baggage compartment just aft of thepilots compartment. If desired, however, it may be advantageouslylocated in the pilots compartment.

From junction box 13, conductors 18, 19, 20, 21 and 22, respectively,associated with the respective bridges in a manner hereinafterdescribed, lead forwardly to a threepole, double throw switch 23provided to enable connecting the indicating means 29 and 24, laterdetailed, into two different circuits with the bridges, in a mannerhereinafter particularized, for respectively indicating the twodifferent sets of loading conditions of the aircraft that the inventionproposes to ascertain.

Switch 23 may be situated either in the pilots compartment or in thebaggage compartment, as desired. The indicating means 24 may consist ofa simple A. C. null-point meter, a dynamorneter type volt meter, arectifier type dArsonval movement, a ratiometer, or, in cases Wheregreater sensitivity may be required, a simple A. C. vacuum tube voltmeter, electrically preceded by an amplifier. In any case, this meter isconnected, at its weight-variable input side, to a pole 26 of the switch23, the other side of the volt meter being connected by means of aconductor 27 and a variable contact 28 with an A. C. potentiometer 29 ofthe rotary slide wire type. As is later partieularized, the slider ofthis potentiometer is mechanically coupled by respective actuatingcouplings to respective indicating dials for separately indicating thetotal loadings and the center of gravity position, of the airplane, asshown in Figure 2. The slide wire of the potentiometer is connected atone end to a switch pole 30, the other end of the slide wire beingconnectible to one side of the energy source. A switch pole 31 isadapted to supply energy thereto from the energy source when the switchis in its full line or rightward position.

Each of the displacement devices indicated within the broken linerectangle 10 preferably comprises a balanced, variable-impedanceelectromagnetic strain gauge 32, shown in Figure 2. The yokes or cores33 of these electromagnetic displacement gauges are, as shown in Figure2, fixedly attached to the inside of one end of each of the axles of therespective landing wheels. In the transport airplane chosen forillustrative purposes, the tricycle landing gear includes a nose wheelaxle 34 and main wheel axles 35. These axles are of the kind adapted toflex upwardly immediately upon increments of loading of the airplane andcontinue flexing upwardly in direct proportion to these increments, in alinear manner.

However, it is to be understood that these yokes may equally well beattached to any other structural member of the landing gear that alsoundergoes immediate deflection in direct and linear proportion toincrements in the weight loading on this structural member.

The armatures of the electromagnets of these displacement devicespreferably take the form of elongated beams 36 and 37 having laminatedextremities 40 and being pivotally mounted to the unloaded, orsubstantially rigid, portions of the nose wheel and main wheel axles,respectively. Since, in the airplane type shown, the nose wheel axle isasymmetrically loaded, a pivot 38 of the beam 36 in the nose wheel axle,is preferably located at a point laterally displaced from thelongitudinal center of both the beam and the axle, for reasonshereinafter particularized, whereas the pivots 39 of the beams 37 in themain wheel axles coincide with the longitudinal centers of both the beamand the axle.

Thermally-induced effects on the field of the electromagnet caused bythe change in length of the beams 36 and 37 may also be anticipated andcompensated for in the manner shown in Figure 4, wherein the yokes 33aare mounted in the axles at right angles to the position they occupy inFigure 2. The yokeward ends 400 of the beams, in this instance arelaminated and constructed of a uniform cross-section throughout theirlengths, this section preferably being that of a square. The two halvesof each yoke are symmetrical, so that thermally induced changes of yokedimensions affect both air gaps equally and hence cause no unbalance ofthe bridges. Expansion and contraction of the beams thus has no effectupon the size of the air gaps and hence thermal influences effect nodetrimental changes in the magnetic field. constancy of performance ofthe electromagnet under all climatic or altitudinous conditions is thusobtained.

In either instance, the other end of each of the beams bears an aperture41 through which extends the shank of an adjusting screw 42 hearingadjusting nuts 43 by means of which the disposition of the ends 40 maybe altered upwardly or downwardly, that is longitudinally of the yokes,to vary the air gaps and the magnetic fields of the yokes, for a purposehereinafter particularized.

In each main wheel 35, the weight of the airplane and its load isapplied at the bottom of the axle and the ground reaction deflects bothends of the axle upwardly. Although the loading of the nose wheel inthis particular type of airplane is asymmetric, both ends of this axle34 are also deflected upwardly. Each of the beams is adapted to add thedeflections occurring at the respective ends of the axles and refers thesum to the yoke end of the axle. As a consequence, only one gauge isrequired in each axle. I a

Each horizontal arm of each pick-up yoke. is provided with an impedancecoil 44, the reactance of each yoke being balanced yet variable, therespective yokes being connected in series to the source of energy byconductor paths 14, 15, and 16. Each of the circuits 14, 15, and 16includes a reactor 45 connected in parallel across the conductor pathand connected in divided circuit by a midpoint tap 45a to the connectedimpedance coils 44. The construction and arrangement of partsestablishes, in association with each axle, a balanced,variable-impedance bridge, composed, in the illustrative embodimentshown, of the yoke 33 and coils 44, the conductor 46 and the dummyreactor 45 with variable center tap resistor 45a, the electromagnetconstituting one-half of the bridge.

Reactive and resistive balance of each bridge is then preferablymaintained by adjusting the nuts 43 at the end of each beam. Theconsequent variation in the disposition at the opposite ends 44 of thebeams within the yoke, varies the air gap thereof and hence effects,through an alteration of the magnetic flux, an adjustment of theimpedance in the impedance coils in such manner as to reestablish thebalance of the unbalanced bridges. Resistive balance is maintainable ineach bridge by suitable adjustment of the mid-point tap of the resistor45a. However, the invention contemplates that, in cases where such maybe found desirable, as shown in Figure 5, a variable potentiometer 47and series connected variable and/or fixed capacitors 48 and 49respectively, may be connected across the supply buses to the input sideof the impedance coils of each bridge. In this case, potentiometer 47 isvariably tapped and series connected to the output side of the impedancecoils, by a conductor 46, through the capacitor circuit. Thisarrangement provides both resistive and reactive balance in the bridge.Reactive and resistive balance of each bridge may also be attained asshown in Figure 6, by mechanically balancing the armature of eachdisplacement gauge with the adjusting screws described and employing aresistive potentiometer like the one designated by numeral 105 in themanner shown.

In either instance, the conductor 46 is rendered integral with a primaryinduction coil 50, which is inductively associated with a secondaryinduction coil 51, the two together establishing a transformer 52.

In order to enable equalization of the voltage outputs of thesecondaries for equal increments of airplane loading, each secondaryinduction coil 51 includes a sensitivity equalizer or adjustablepotentiometer 53 connected in parallel across the output terminalsthereof. Respective conductor paths A, B, and C lead from the respectivesensitivity equalizers toward the switch 23, volt meter 24, andindicating devices 68 69 in a manner and for a purpose hereinafterparticularized.

The illustrated mode of taking off the voltage outputs of the bridges,while replaceable by equivalent modes, is the preferable form, as itenables mixing the bridge outputs in an easy manner to facilitateascertaining both the loading and the center of gravity position of theairplane, by simple indicating devices and by a relatively small numberof circuits thereto. This arrangement also enables the employment ofsensitivity equalizers which, after the adjustment to the same absolutesensitivity in each bridge, may be hermetically sealed and remainwithout recalibration or other attention for long periods of time.

In the preferred embodiment all components of the bridges, save thedisplacement gauges, the reactors, and the transformer couplings, areadvantageously locatable in the junction box 13.

Although it is preferable to employ a transformer coupling to take-offthe voltage outputs of the bridges, the invention also contemplates theemployment in their stead in each bridge, as shown in Figure 3, of aseparate sensitive null-point volt meter 54 and a rotary slide wirepotentiometer 55 for individual indication of the loading-induced outputof each bridge. The three readings may either be added by the pilot orfreight master, or compared in ratio by him to determine either thetotal loading, or the center of gravity position, of the airplane.

By the aforesaid manipulation of the adjusting nuts and the reactor tapsaforedescribed, the bridges are adapted to be brought into a balancedcondition at the inception of the loading operations. Thus, the bridgesat this juncture, that is, when the airplane is in the empty condition,produce zero output voltage. As the loading operations proceed, however,increments of load effect axle deflections, causing relative movement ofthe beams with respect to their yokes and varying the air gaps thereof.The resultant change in the magnetic fluxes of the electromagnets altersthe impedance to the alternating current in the two impedance coils ofeach electromagnet in opposite directions and unbalances the bridge. Avoltage is thereby impressed upon the primary of each couplingtransformer in each bridge. If the switch 23 then occupies its rightwardposition, shown in full lines in Figures 1 and 2, the voltage outputfrom the sensitivity equalizer of the nose wheel bridge is therebyimpressed, via the conductors 56 and 57, upon the sensitivity equalizer53 of the left hand main wheel, as shown in Figure 2. The compoundedvoltages lead therefrom through a conductor 58 to the sensitivityequalizer 53 of the right main wheel and thence through conductor 18 tothe pole 26 of switch 23. Equal voltage outputs and equal increments ofloading are assured by adjustment of the adjustable contacts of thesensitivity equalizers in the manner aforedescribed.

The phase of the voltage applied from the energy source to the slidewire is to be shifted in such manner as to throw it into phase with theoutputs from the gauges, when any type of mentioned meter 24 except aratiometer is employed. To this end, a phase-shift network generallydesignated in Figure 2 by reference numeral 59 has its input sideconnected in parallel with the common supply busses for all the bridgesand its output end connected in series with switch contacts 60 and 61.The network chosen for purposes of exemplification includes atransformer 62, the primary of which is connected directly across thesupply busses, the secondary thereof including a capacitor 63 and avariable resistor 64 and in divided circuit with contact 60 of theswitch. A midpoint tap 65 is associated with the secondary of thetransformer and is connected to contact 61 of the switch.

Regardless of the particular type of phasing means employed, with switch23 in the rightward position, the voltage outputs of the three couplingtransformers are added in phase at the weight-variable input side of thesensitivity meter 24, the sum being directly proportional to the loadingof the airplane at any given stage of the loading operations.

With these relationships establishable in this manner, in order toascertain the total loading of the airplane it is only necessary toplace switch 23 in its rightward position and to manipulate the sliderof the slide wire potentiometer or its equivalent to null the reading ofthe nullpoint meter 24. The loading of the airplane or other vehicle canthen be directly read from a dial 68 calibrated in pounds andmechanically coupled to the slider of the slide wire potentiometer inthe manner customary in these conventional indicating devices.

With switch 23 in its leftward position, shown in dotted lines in Figure2, voltage induced in the sensitivity equalizers 53 of the nose wheelbridge is impressed, singly, upon contact 67 of switch 23 throughconductors 56 and 66, designated together as 19 in Figure l. Thence thisvoltage is applied through conductor 25 to the weightvariable input sideof the volt meter 24. At the same time, the center arm is disconnectedfrom contact 61) and contacted with the ground pole G, switch pole 30occupies a disconnected position with reference to the sup ply line 21from the energy source and is now connected with contact 67a of theswitch. The slide wire 29 is thereby disconnected from the energy sourceto which it was initially connected via the phase-shifting means 59 andconnected to the voltage from the bridge of the left hand Wheel and fromthe bridge of the right main wheel via conductor 22. The compoundedvoltages are applied through contact 23 and conductor 27 to theresistancevariable input side of the meter 24.

With the circuits in this relationship, the rotary slide wire 29 isconstituted a potentiometer with reference to the outputs of the nosewheel bridges and the main wheel bridges. When the potentiometer 29 isso adjusted as to null the volt meter, the pointer 28 will indicate theratio between the sum of the outputs of the main wheel bridges and theoutput of the nose wheel bridge.

To ascertain the longitudinal position of the center of gravity of theairplane as a percentage of the mean aerodynamic chord, switch 23 isreadily shifted to its leftward position, and the rotary slide wire isadjusted to null the volt meter. The position of the pointer 28 withrespect to a dial 69, calibrated in percentage of the mean aerodynamicchord and also separately mechanically coupled to the slider of theslide wire, gives a direct indication of the longitudinal position ofthe center of gravity. Dial 69 is preferably calibrated with respect tothe specific loading moments of the airplane and bears suitable markingindicating the safe loading limits of the airplane for maintainingstability.

Adjustment of the slider of the potentiometer 29 in milling the voltmeter 24 does not balance the bridges. It is therefore preferable thateach gauge be constructed to have identical non-lincarities ofperformance; or, more preferably, that they operate linearly over theentire range. With either of these conditions, it is advantageous toinclude a sufiicient amount of molybdenum permalloy in each yoke tomaintain the permeability of its iron circuit constant over alltemperature conditions.

With the longitudinal centers of the main wheel beams located, asdescribed, concentrically with the longitudinal center of theircorresponding axles, uneven footing of the tires of the dual mainwheels, although inducing variations in tire loads, will have noappreciable effect upon the deflections of the beams. For types ofairplanes in which the nose wheel axle is asymmetrically loaded, thelocation of the fulcrum of the beam of the nose wheel displacement gaugeat a point laterally offset from the center of both the beam and theaxle, is highly advantageous in that it maintains the total deflectionsof the beam, referred to the yoke, substantially independent of sideloads on the nose landing leg. In addition, relatively minutedeflections of the axle produce, in such an arrangement, relativelylarge deflections of the beams, rendering the device sensitive to theslightest change of loading of the aircraft.

As manifested, the present invention is not limited to that embodimentin which the displacement device in the bridge is an electromagnetictype of strain gauge. However, such type is preferable for many reasons,among which is the fact that electromagnetic displacement devices of thepresent type have an effectively much longer gauge length than othertypes and hence will discern a smaller increment of loading than suchdevices as the resistance wire type of strain gauge.

The invention, as should now be clear, is also not limited to theemployment therewith of a null-point volt meter and rotary slide wire toelectrically measure the axle deflections in the manner aforedcscribed,inasmuch as a direct reading galvanometer may be employed for thispurpose if desired. However, the employment of the present null-pointtype of volt meter and rotary potentiometer is quite advantageous,inasmuch as a null-point volt meter permits a very wide swing of theneedle, enabling a high degree of accuracy in indicating the bridgeratioset up thereat in determining the position of the center of gravity.

Many refinements and ramifications of the preferred embodiment areincluded within the scope of the inventive concepts. For instance,intsead of being located as shown in Figure 1, all the components of theapparatus except the displacement gauges and the energy source, may belocated at one and the same station in the airplane. That is, thejunction boX, switch, sensitivity meter, and rotary slide wire may beall located together either in the baggage compartment, for theconvenience of the freight master, or in the pilots compartment toenable him to supervise loading operations.

I claim:

1. In apparatus for determining the weight of '8. vehicle havingground-engaging means, a weight-responsive strain-gauge unit, including:a substantially 'hollow axle in the ground-engaging means adapted to bedeflected in direct proportion to the weight of the vehicle; an elongatearmature disposed coaxially in said axle and pivoted transverselythereto, one end of said armature undergoing relative movements withrespect to said axle that are in direct proportion to the weight-causeddeflections of said axle; electro-magnetic pick-up means mounted fixedlywith respect to said axle operatively adjacent one end of said armatureand adapted to emit a signal varying in strength in direct proportion tothe relative movements of said armature; and weight indicating means incircuit with and actuated by said pickup means.

2. An indicating device comprising: means for supplying electricalenergy; a plurality of means defiectible in direct proportion toincrements of weight loading thereon; means electrically connected tothe energy supply for establishing a plurality of normally balancedelectrical bridges, each including the winding of an electromagnet;means displaceablc relative to each of said windings by deflection ofsaid deflectible means to unbalance and thereby set up a potentialacross the midpoints of the bridges; means inductively responsive toeach of said potentials for producing proportionate potentials; a nullpoint voltage meter; a slide wire potentiometer having a resistor; meansfor summating the inductively produced potentials and passing thesummation through the meter to the potentiometer slider, thence throughone end of the potentiometer resistor; and means subjecting the resistorto the supply potential; the movement of the slider to null the meterupon the occurrence of an unbalanced bridge indicating the weightcausing such unbalance.

3. Apparatus for indicating the weight loading of a vehicle having aplurality of ground engaging means and a source of electrical energy,comprising: a first member in each of said ground engaging meansflexurally responsive to increments of loading of the vehicle and havinga nonflexing mid-point; a second member pivoted at the non-flexingmid-point of each of said first members and being immovable with respectto one end of said first member whereby the second member is relativelydisplaceable with respect to the other end of said first member bydeflections of both ends of the first member, a free end of each secondmember being of magnetic material; an electromagnet fixedly mounted onsaid other end of each of said flexural members and magneticallyaffected by movement of said pivoted member; normally balanced bridgemeans, one path of each consisting of the windings of one of theelectromaguets; means responsive to the potential across the bridgemidpoints upon the unbalancing of the bridges due to flexure in theflexural members; and means indicating the summation of the effects onthe potential responsive means.

4. In an indicating device, a hollow flexural member deflectable byincrements of weight loading thereon; a source of electrical energy; anelectromagnet including plural windings and an air gap fixedly mountedat one end of the flexural element and energized by said source; anelongate armature member pivotally supported within the flexural memberat a non-flexing mid portion thereof and having one end extending intothe air gap; a post carried by said flexural member at the other end ofthe fiexural member passing transversely through said elongate member;adjusting nuts on the post to move the elongate member about its pivotwhereby the position of the end of the elongate member within the airgap may be varied.

5. Apparatus for determining the weight of a vehicle, comprising: groundengaging means operatively associated with said vehicle; deflectiblemeans operatively associated with said ground engaging means anddeflecting in proportion to the vertical loads on said ground engagingmeans; a source of electrical energy; normally balanced bridge circuitsconnected to said source; strain gauges forming a first half of each ofthe bridges, said gauges including electromagnets and components carriedby said deflectible means for varying voltages in the electromagnets;means inductively energized in response to the voltage across each ofthe bridge midpoints when said bridges become unbalanced due to voltagechanges in the electromagnets; null point indicating means; apotentiometer including a slider and a resistance; conductor pathssummating the outputs of the inductively energized means, passing thesummation through the indicating means, the slider, and one terminal ofthe potentiometer resistance; a circuit from said energy source throughthe resistance of the potentiometer, whereby movements of the sliderupon a change in output of the inductively energized means eflects anulling of the indicator means, said movements indicating the change invehicle weight.

6. Apparatus for determining the weight of a vehicle, comprising: groundengaging means operatively associated with said vehicle; weightdeflectible means in said ground engaging means; a source of electricalenergy; normally balanced bridge circuits connected to said source, oneside of each of said bridge circuits including a component having thevoltage thereacross varied in proportion to the deflection in saidweight deflectible means; means electrically connecting theequipotential midpoints of each of the balanced bridges; meansinductively energized by the potential across the bridges when saidbridges are unbalanced; nullpoint indicating means; a potentiometerhaving a slider and a resistance; conductor paths serially connectingthe inductively energized means, impressing the output thereof throughthe indicating means, the slider, and one resistor terminal of thepotentiometer; a circuit from said energy source through the resistor ofthe potentiometer whereby movement of the slider upon a change in outputof the inductively energized means will null the reading of theindicating means.

7. Apparatus convertible from a weight indicator to a center of gravityindicator for use on vehicles, comprising: front and rear groundengaging means respectively spaced along the longitudinal axis ofsymmetry of the vehicle and fore and aft of the center of gravitythereof; weight deflectible means in each ground engaging meansdeflectible in direct proportion to the loads thereon; an electricalenergy source; strain gauges energized by said source in each saidweight deflectible means producing potentials proportionate to theloads; conductor paths summating the potentials; a null point meter; apotentiometer having a resistance and a slider to pick off the varyingpotential along the resistance; a double throw switch in one positionconnecting the energy source through the resistance of the potentiometerand connecting the summated potentials through the meter to the sliderthence returning through one end of the resistance, said switch in itsother position connecting the summated potentials through the resistanceand connecting the meter in circuit with its one side subjected to thepotential at the slider and its other side subjected to the potentialproduced by the strain gauges in the front ground engaging means, theposition of the slider when the meter is nulled providing an indicationof the weight and the relative postion of the center of gravity betweensaid ground engaging means and along said axis of symmetry respectivelyof the vehicle in the first and other said positions of the switch.

References Cited in the file of this patent UNITED STATES PATENTS Re.14,475 Troll May 21, 1918 1,407,078 Murray Feb. 21, 1922 1,864,876Westrum June 28, 1932 2,159,373 Dunn May 23, 1939 2,260,036 Kuehni Oct.21, 1941 2,276,817 Bagno Mar. 17, 1942 2,336,371 Shayne et a1 Dec. 7,1943 2,394,079 Langer et al. Feb. 5, 1946 2,540,807 Berry Feb. 6, 19512,559,718 Goodlett et a1 July 10, 1951 2,577,691 Shrader et a1 Dec. 4,1951 2,615,330 Blackmon et al. Oct. 28, 1952 FOREIGN PATENTS 215,986Great Britain May 27, 1924

